The field of this invention relates to electrical apparatuses and methods for permanent removal of undesirable hair on human beings.
Procedures and apparatus for the removal of unwanted hair on human beings has long been known in the cosmetic art, the goal being to improve the patient's appearance. The prime objective of such procedures is the permanent removal of the hair as a result of a single application. Hair removal applications normally accomplish this objective by destroying the hair follicle from which the hair grows. To avoid unsightly scarring and to increase the patient's comfort during hair removal procedures, procedures to destroy a hair follicle have to be accomplished with a minimum amount of destruction of the tissue surrounding the follicle and a minimum level of patient discomfort and pain during and after the procedure.
For a great many years, direct current electrolysis has been used for permanent hair removal. The direct current produces a chemical reaction in and around the follicle, the main product of which is sodium hydroxide, or lye. This sodium hydroxide is an aggressive chemical that completely destroys the hair.
The main advantage of direct current electrolysis is a low rate of re-growth. Nevertheless, the method has certain disadvantages. First, direct current electrolysis requires the application of the current for a substantial period of time (one to three minutes) for each hair follicle. Also, direct current electrolysis is somewhat painful to the patient.
In recent years, a new electrolysis technique, called “thermolysis” became prevalent in this arena. Thermolysis uses a probe in the same manner as direct current electrolysis and also removes a single hair at a time. With thermolysis, however, radio frequency radiation—not direct current as in direct current electrolysis—is applied to the follicle. Over a period of several seconds the radio frequency energy thermally coagulates the follicle, thereby destroying it and preventing it from subsequently regrowing.
A disadvantage of thermolysis as a technique for hair removal is that the heating pattern is narrow. Consequently, it has been generally found that thermolysis has a low reliability factor when used on heavy hair due to the fact that heavy hair follicles are too wide for the heating pattern. The technique also has a low reliability factor when used with curly hair because the follicle itself will curl away from the probe and thereby leave hair follicle areas that have not been destroyed. Any portion of the hair follicle that has not been destroyed will be capable of re-growing hair.
Consequently, despite the prior art, a need still exists for a hair removal device that produces long-lasting results and is simple, fast and easily manipulated by the user. As disclosed herein, applicants' propose apparatus and method utilizing “electroporation” to satisfy that need.
The term electroporation (sometimes referred to hereafter as “EP”) is used herein to refer to the use of a pulsed electric field to induce microscopic pores in the membranes of living cells. Living cells include a biological membrane, also commonly called a cell wall, which separates the inner volume of a cell, or cytosol, from the extracellular space, which is filled with lymph. This membrane performs several important functions, not the least of which is maintaining gradients of concentration of essential metabolic agents across the membrane. This task is performed by active protein transporters, built in the membrane and providing transport of the metabolites via controlled openings in the membrane. Inducing relatively large pores in the cell membrane by electroporation creates the opportunity for a fluid communication through the pores between the cytosol and the extracellular space that may lead to a drastic reduction of these vitally important gradients of concentrations of the metabolic agents. Uncontrolled exchange of metabolic agents, such as ions of sodium, potassium, and calcium between a living cell and the extracellular space imposes intensive biochemical stress on the cell.
When a cell is experiencing biochemical stress the major biochemical parameters of the cell are out of equilibrium and the cell cannot perform its routine functions. In an attempt to repair itself, the cell starts working in a damage control mode to restore the cell to its normal biochemical equilibrium by transporting metabolic agents or chemicals across the cell membrane into and out of the cell. The active protein transporters (or pumps), which routinely provide transport of various metabolic agents, especially proteins, across membranes, use the energy of hydrogen or sodium positive ions passing from the positive potential of the intracellular space to the negative potential of the cytosol for transport of metabolic agents into the cell, or the energy of a negative chlorine ion for transport of metabolic agents in the opposite direction out of the cell. This energy supply is provided by maintaining the potential difference across the membrane at a particular level, which, in turn, is linked to the difference in concentrations of sodium and potassium ions across the membrane. When the potential difference across the membrane is too low, thousands of the active transporters find themselves out of power and the cell finds repair difficult and in some cases unlikely if not impossible as the intracellular space is invaded by extracellular chemicals.
Invasion by high concentrations of calcium ions from the interstitial space between cells, where the calcium ion concentration is about 10,000 times higher than in the cytosol, triggers an emergency production of actin filaments across the large pores in the membrane in an attempt by the cell to bridge the edges of the pores, pull the edges together, and thereby seal the opening in the membrane. In muscle cells the calcium ion invasion may cause lethal structural damage by forcing the cell to over-contract and rupture itself.
As noted earlier, the application of a pulsed electric field can create membrane pores. Small pores in the membrane created by a relatively short electric pulse can reseal themselves spontaneously and almost instantaneously after the removal of electric field. No significant damage to the cell is done in this case. Contrary to that, larger pores may become meta-stable with very long life time and cause irreversible damage to the cell. It can be said that, depending on the number, effective diameter and lifetime of pores in the membrane, electroporation of the cell may result in significant metabolic or structural injury of the cell and/or its death. The cause of cell death after electroporation is believed to be an irreversible chemical imbalance and structural damage resulted from the fluid communication of the cytosol and the extracellular environment.
Below a certain limit of the electric field no pores are induced at all. This limit, usually referred to as the “lower EP limit” of electroporation, is different for different cells, depending, in part, on their sizes in an inverse relationship. That is, pores are induced in larger cells with smaller electric fields while smaller cells require larger electric fields. Above the lower EP limit the number of pores and their effective diameter increase with both the amplitude and duration of the electric field pulses.
Removing the electric field pulses enables the induced pores to reseal. This process of resealing of the pores and the ability of the cell to repair itself, discussed briefly above, currently is not well understood. The current understanding is that there is a significant range of electric field amplitudes and pulse durations in which cells survive electroporation and restore their viability thereafter. An electroporated cell may have open pores for as long as many minutes and still survive. The range of electric field amplitudes and pulse durations in which cells survive is successfully used in current biomedical practice for gene transfer and drug delivery inside living cells.
Nevertheless, the survivability of electroporated cells is limited. As the electric field amplitude and/or duration of pulses, increases, this limit, usually referred to as the “upper EP limit” of electroporation, is inevitably achieved. Above the upper EP limit, the number and sizes of pores in the cellular membrane become too large for a cell to survive. Multiple pulses cause approximately the same effect on the cells as one pulse with duration equal to the total duration of all applied pulses. After application of an electrical pulse above the upper electroporation limit the cell cannot repair itself by any spontaneous or biological process and dies. The upper EP limit is defined by the combinations of the amplitudes of electric field and pulse durations that cause cellular death.
The susceptibility of cells to electroporation depends on their size: the larger the cell, the lower the electric field and duration of a pulse capable of creating electropores. If cells of different sizes are exposed to the same electric field, the largest cells will have pores opened first and will die first if the electric field applied is above the upper limit of electroporation. The ability of electroporation to discriminate cells by their sizes is important feature of the phenomenon and may be used to selectively kill large cells in the human body.
The use of electroporation to kill cells of various types has been proposed in the prior art. For example, in U.S. patent application Ser. Nos. 20040019371 and 20030153960 filed by the same applicants as the present invention, the use of electroporation above the upper limit is proposed for killing fat tissue and in U.S. patent application Ser. No. 20030060856, also filed by the same applicants as the present invention, the use of electroporation above the upper limit for prostate tissue is proposed to treat benign prostatic hyperplasia. Applicants are unaware of any proposal to use electroporation as a hair removal technique.
Usually, electroporation of biological cells implies the application of high voltage pulses longer than a microsecond. This duration is stipulated by the time of relaxation of the cell membrane equal approximately 1 microsecond. In U.S. Pat. No. 6,326,177 B1 issued to Schoenbach et al. a method of electroporation employing ultrashort electric field pulses. The duration of these pulses is not enough to disrupt the cell membrane as described above, but they are capable of disruption of the subcellular structures that leads to the cell death. This method of using ultrashort pulses is proposed for use in killing cancer cells, though the patent also claims applicability to fat cells, bone cells, vascular cells, muscle cells, and cartilage cells.
One potential side effect of the use of electroporation in the removal of unwanted body hair is that some patients may experience some level of discomfort. The electroporation in-vivo of hair involves high voltage pulses applied to the skin of a patient. Delivery of such pulses, however, may result in the patient experiencing an unpleasant sensation of small, but palpable electric jolt or shock during pulsing. It would be desirable to provide relief from such sensations during a hair removal procedure using electroporation. Applicants propose providing such relief with non-invasive, non-drug apparatus and method that provide, if desired or necessary, transcutaneous electrical nerve stimulation (TENS) during the hair removal process.
TENS is one of the available non-drug mediated pain control techniques. It is based on a discovery that application of electrical current to the body can also interfere with transmission of pain signals along the nerve pathways and give patients a significant analgesic (pain relieving) effect. The Gate Control Theory of pain suggests that this effect is mediated by endogenous pain relieving chemicals, released by the body in response to the electric transcutaneous stimulation, consequently blocking the ability of the nerve to transmit pain signals. If a large nerve, responsible for transmission of perception of heat or touch, is carrying periodic signals from the endings on the skins, the Gate for the pain signals transmitted to the spinal cord via small nerves are closed and the pain is reduced.
Currently TENS is used primarily for symptomatic relief and management of chronic intractable pain or as an adjunctive treatment in the management of post-surgical or post-traumatic acute pain. TENS usually involves the application of a sequence of short electrical pulses with a relatively low repetition rate intended to affect the nervous system in such a way as to suppress the sensation of pain from acute or chronic injury. Typically, two electrodes are secured to the skin at appropriately selected locations. Mild electrical impulses are then passed into the skin through the electrodes to interact with the underlying nerves over the treatment site. As a symptomatic treatment, TENS has proven effective in the reduction of both chronic and acute pain of patients.
In summary, while the prior art teaches apparatus and methods for the removal of unwanted body hair, the prior art suffers from the disadvantages discussed above. It would be desirable to have apparatus and method that could provide hair removal without being subject to those disadvantages and that could, if desired or necessary, mitigate any discomfort created by the electroporation in-vivo procedure without resorting to pharmacological aids.